1. Field of the Invention
The present invention relates to a raw-material heating apparatus, and more particularly to a vertical-type raw-material heating apparatus for heating a raw material such as a raw ore prior to effecting heat treatment such as maturing.
2. Description of the Related Art
As an apparatus of this type, for example, one shown in the appended drawing FIG. 5 is known. In this known apparatus, a heating section A is formed by an upper portion above a hearth 51, while a vertical-type hollow cylindrical member 53 communicating with a lower portion therebelow by means of a drop port 52 in the hearth 51 is disposed below the heating section A so as to form a maturing section B for maturing and cooling the raw material.
The hearth 51 of the above-described known apparatus rotates about a vertical axis 58A, and rod-like pushers (material pushing-in devices) 54 for allowing a deposited layer of a raw material M formed on a hearth surface 51A to drop gradually through the drop port 52 which is open in the center are provided above the hearth 51.
A heating gas (mainly a combustion gas) is supplied from a heating-gas blowing pipe 58 to a heating space 57 formed in such a manner as to be surrounded by a furnace cover 55, a peripheral wall 56, and the hearth 51. The raw material M in a deposited layer surface M1 on the hearth 51 is directly heated by the heating gas, and its temperature rises. The heated raw material M in the deposited layer surface over the hearth 51 drops into the vertical-type hollow cylindrical member 53 from the drop port 52 by the action of the pushers 54, thereby forming a deposited layer M2 inside the hollow cylindrical member 53.
As also shown in FIG. 6, which is a cross-sectional view taken along VI--VI in FIG. 5, the aforementioned rod-like pushers 54 are provided at a plurality of circumferential positions (incidentally, in FIG. 6, the drop port 52 located below the cross-sectional line VI--VI in FIG. 5 is shown by a two-dot chain line for reference sake). In the case illustrated in FIG. 5, the timings of operation of the plurality of pushers 54 are alternately staggered. Each pusher 54 has an effective region E for effectively feeding the raw material to the aforementioned drop port 52 through its movement in a direction toward the drop port 52 (in the longitudinal direction of the pusher 54). An ineffective region N is formed between adjacent ones of the effective regions E. When viewed from above, raw-material supplying pipes 59 for supplying the raw material M onto the hearth 51 and exhaust pipes 60 are connected to the furnace cover 55 in such a manner as to be located in the aforementioned effective regions E and in the ineffective regions N, respectively.
Next, in FIG. 5, cooling air is supplied from below into the deposited layer M2 inside the hollow cylindrical member 53 which forms the maturing section B. The raw material which constitutes this deposited layer M2 drops while maturing by means of the heat which it possesses, is gradually cooled by heat exchange with the cooling air, and is removed as a product from a discharge port (not shown) in a lower portion of the hollow cylindrical member 53. Meanwhile, the aforementioned cooling air rises through the aforementioned deposited layer M2 while being heated by the raw material, and flows into the aforementioned heating space 57 in the state of increased temperature, thereby contributing to the combustion of the heating gas.
In addition, the heating gas inside the heating space 57 enters the interior of the deposited layer of the raw material M on the hearth 51 from the deposited layer surface M1, and after heating the raw material M in the interior, the heating gas passes through the exhaust pipes 60, and is discharged to the outside as an exhaust gas.
With the above-described known apparatus and numerous other apparatuses similar thereto, the pushers are provided at a plurality of circumferential positions such that the rod-like pushers are capable of reciprocating in their longitudinal directions (i.e., in the radial direction of the hearth) and are arranged radially from a central portion of the hearth. When the pushers advance toward the opening formed in the central portion of the hearth, the pushers operate to push out the raw material to the opening, and this pushing out of the pushers acts effectively with respect to the raw material in regions each having a circumferentially fixed width. Namely, the effective regions having the aforementioned widths are present at a plurality of circumferential positions above the hearth, while the ineffective regions where the pushers exhibit no effect during their operation and the raw material does not move much are respectively formed between adjacent ones of the effective regions. These ineffective regions expand larger on the outer peripheral side as compared to the inner peripheral side of the hearth.
In the effective regions, the raw material moves effectively toward the drop port, and is replaced by new raw material which is consecutively supplied from the raw-material supplying pipes disposed in the effective regions. In contrast, since the exhaust pipes are located in the ineffective regions, the high-temperature gas from the heating space passes through the material in the ineffective regions and reaches the exhaust pipes, so as to heat the raw material in the ineffective regions which does not move much. Namely, in the effective regions, since the raw material moves despite the fact that the high-temperature gas does not actively flow into these regions, a large difference is produced in the degree of heating as compared with the raw material in the ineffective regions. That is, a difference is produced in the degree of heating depending on whether the raw material is located in the effective regions or the ineffective regions. In addition, since the high-temperature gas passes through the raw material in the ineffective regions which does not move much and is at the high temperature, the high-temperature gas is discharged from the exhaust pipes without having undergone sufficient heat exchange with the raw material, so that the thermal energy is not sufficiently utilized.